Method and means for removal from and burning of ash on a grate



Dec. 19, 1950 c H SPARKS 2,534,634

METHOD AND MEANS FOR REMOVAL FROM AND BURNING OF ASH ON A GRATE Filed Nov. 9, 1946 FTTA F/Y YS,

Patented Dec. 19, 1950 METHOD AND MEANS FOR REMOVAL FROM ANDBUR'NING' OF ASH. ONA GRATE Cedric H. Sparks, London, England, assignor to Detroit Stoker Company, Detroit, Mich, a corporation of Michigan Application November 9, 1946,.SerialN0. 708,976: In Great Britain October 1,1945

Section 1, Public Law 690, August 8, 1946 Patent expires October 1, 1965 6 Claims.

This invention relates to stokers and particularly to sprinkler stokers, an object being the provision of improved means for removing ash from. the grates of: sprinkler stokers. A further object is to enable a high percentage ofv the carbon contained in the ash to be consumed.

The present invention includes a sprinkler stoker, comprising an ash conveyor including means adapted, by moving over the stoker grate, to gather ash from below the fuel bed on the grate and discharge the ash from the grate at an end thereof.

The invention also includes the method of burning solid fuel which comprises sprinkling fuel onto a grate, drawing ash from below the: fuel bed on the grate to an end. of the. grate, supplying air separately to the said end of the grate in order to burn thereon residual combustible material in the ash and subsequently discharging the ash from the end of the grate.

The invention will now be described, by way of example, with reference to the accompanying partly diagrammatic drawing showing in sectional side view a boiler furnace chamber fitted with a sprinkler stoker.

In the drawing, the furnace chamber 1 is formed with a top gas outlet across which extends a bank of tubes 2 and with rear, side and front walls 3, 4, and 5' respectively. To the front wall 5- is fitted sprinkler mechanism 6, of

any suitable construction, adapted to discharge fuel through an aperture 1 onto a grate 8. At the front of the furnace chamber is an arch 9, below which is an ash pit in closed by an appropriate door or doors for the removal of ash.

Provision is made for supplying combustion air to the space H below the grate 8, and below a front portion of the grate beneath the arch 9 is a compartment [2 the air supply to which is separately controlled and is preferably at a higher pressure than the air supply to the space H. A separate or booster fan may be used for supplying the air at higher pressure. The bars of the grate 8, will generally be fixed relatively to one another, but, if desired, suitable means may be provided for imparting thereto relative oscillatory movements, with the object of maintaining clear the air passages between the bars.

Arranged to reciprocate on the grate 8, longitudinally thereof, is a transverse drag member 13 shaped to exert a cleaving action on the fuel bed when moving from front to rear of the grate and a dragging action on the ashes at the bottom of the bed when moving from rear to front of the state.

2. angular cross-section, the. rear or main upper face [4- being inclined at a smallangle to the base, and the minor or front upper face l5 being inclined at a much larger but nevertheless acute angle to-the base.

The drag member i3 is secured at its centre to an endless chain it arranged. to run in a groove formed in the grate 8 at the top thereof. The chain is built of links having their upper edges flush with the upper surface of the grate and are adapted to fill the groove, so as to make the upper surface of the grate continuous over the full grate area and substantially to seal the groove against ash infiltration.

The. chain It passes. around a sprocket H at the rear of the grate and a sprocket l8 at the front of the grate: andthe sprocket. I8 is associated' with appropriate driving means such as a reversible electric motor not shown operating through. reduction gearing and a chain drive I9. The sprockets are disposed outside the furnace and are enclosed in gas-tight casing-s and the furnace rear wall 3 and the wall 29 below the arch 9 are formed with suitable ducts for the passage of the chain.

If the drag member 13 is of more than. a moderate length it may be secured to two or more chains spaced apart and associated with sprockets one common driving shaft.

Above the ash pit [0 are provided transversely spaced, longitudinally extending rails or slide bars 2| for supporting the. drag. member 13 and a suitable guard not shown is arranged to protect the chain is from ashes discharged from the end of the grate 8. Normally the drag member is stationary and rests on the rails 2| and is screened to a large degree from the heat of the furnace by the arch 9.

During operation, the sprinkler mechanism 6 throws fuel into the furnace chamber A and particles. of fuel fall upon the grate 8, but that portion of the grate above the compartment l2, being below the arch 9, receives substantially no fuel and the supply of combustion air to the compartment is cut off. Air, however, is supplied to the space H and the fuel supplied by the sprinkler mechanism burns partly in suspension and partly upon the grate 8, the ashes from the fuel burned on the grate forming an ash layer between the live fuel and the surface of the grate.

When the grate 8 is to be cleared of ash, the driving. means is operated to move the drag member l3- rearwardly until it reaches the back end of the grate, whereupon the driving means Suitably, the drag member is of triis stopped. Owing to the small acute angle between the base and the rear upper face M of the drag member, the latter, during the rearward movement, cleaves through the ashes on the grate substantially without moving them rearwardly.

Directly after the drag member l3 has been stopped at the rear end of the grate, the driving means is restarted in the reverse direction, so that the drag member moves forwardly and drives before it, over the grate, ash below the burning fuel. The forward movement is continued until the drag member has pushed the driven ash onto the portion of the grate above the compartment [2, whereupon the forward movement of the drag member is stopped, and combustion air is admitted to the compartment, with the result that any carbon remaining in the ash is rapidly consumed.

When the combustion of the carbon in the ash is complete, the supply of air to the compartment [2 is discontinued and the forward movement of the drag member is resumed, so that the ash is dragged forwardly and falls into the ash pit Ill. When the drag member reaches its normal position below the arch 9, the driving means is stopped. The operating cycle described is repeated whenever the amount of ash on the grate necessitates clearing ash therefrom.

When an electric motor is used for driving the drag member, the motor may be provided with control gear adapted automatically to reverse the motor when the drag member reaches its rearmost position and to stop the motor when the drag member, in traveling forwardly, has reached a position at or adjacent the portion of the grate above the compartment l2 and again has reached its normal position beneath the arch 9. Means, such as a pointer shaped like the drag member and arranged to move relatively to a representation of the grate, may also be provided for showing the position of the drag member relatively to the grate.

When the grate is of a substantial width, the grate may be sectionalized across its width, each section being provided with an individual drag member. Such drag members may be operable simultaneously or separately. For example, each section of the grate may be supplied separately with air, and may be provided with individual sprinkler mechanism and with an individual and separately operable drag member.

In the sprinkler stoker described above, a grate of simple construction is used and the ash removing means is also of a simple but effective nature and may be operated without discontinuing the supply of fuel to and the combustion of fuel on the grate. The maintenance of the ash removing means is facilitated, since it operates only intermittently and for short periods of time so that wear of the parts is minimized and since the moving parts thereof may be readily replaced. As the drag member extracts ash from below the burning fuel, the surface of the grate and the part of the chain within the roove in the grate, after an ash extracting operation, remain covered and protected from radiation within the furnace. The stoker also possesses the advantage that the ash is discharged at the front of the grate so that no space is required at the back of the grate for an ash hopper. Moreover, the provision below an arch of a portion of the grate having a separate air compartment enables substantially the whole of the carbon in the ash to be burned.

It would, of course, be possible to arrange for a drag member to be moved from the rear to the front Of a grate by an endless chain driven unidirectionally, but then openings at the rear and front of the furnace for the passage of the drag member into and out of the furnace would be necessary, as well as suitable sealing means adapted to permit the passage of the drag member through but normally to seal the openings.

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we claim is:

1. The method of burning solid fuel which comprises sprinkling fuel onto a grate, moving ash from below the fuel bed on the grate to an end portion of the grate, supplying air separately below the said end portion of the grate at a pressure higher than that at which it is supplied below the adjacent part of the grate in order to burn thereon residual combustible material in the ash and subsequently discharging the ash from the end portion of the grate.

2. The combination in a furnace, of a stoker grate upon which solid fuel is adapted to burn, means providing an ash pit at one end ofthe grate into which ash may be discharged, conveyor means including a drag member arranged. transversey of the grate and reciprocable longitudinally over the grate and ash pit for gathering ash from below the fuel bed on the grate and discharging it into said ash pit, and arch means over the ash pit and forming a screen over the drag member when the latter is disposed over the ash pit.

3. The combination in a furnace, of a stoker grate upon which solid fuel is adapted to be burned, conveyor means including a drag member arranged transversely of the grate and reciprocable longitudinally thereof for gathering ash from below the fuel bed on the grate and discharging it from the grate at one end thereof, means providing a space below the grate for supplying air through the grate and to the fuel, means providing a separate passage under a portion of the grate adjacent said discharge end for supplying air at a higher pressure to any fuel dragged over said grate portion above the separate air passage, and screen means in the form of an arch extending over said grate portion.

4. A sprinkler stoker comprising an ash conveyor including a transverse drag member adapted, by moving over a stoker grate, to gather ash from below the fuel bed on the grate and discharge the ash from the grate at one end thereof, said drag member being arranged to reciprocate on the grate longitudinally thereof and shaped to exert a cleaving action when moving away from the discharge end of the grate and a dragging action when moving towards the discharge end of the grate, and an arch extending above an ash pit at the discharge end of the grate and serving as a screen below which the drag member may normally rest.

5. A sprinkler stoker comprising an ash conveyor including a transverse drag member adapted, by moving over the stoker grate, to gather ash from below the fuel bed on the grate and discharge the ash from the grate at one end thereof, said drag member being arranged to re ciprocate on the grate longitudinally thereof and shaped to exert a cleaving action when moving away from the discharge end of the grate, and an arch extending above an ash pit at the discharge end of the grate and serving as a screen below which the drag member may normally rest, and means for separately controlling an air supply to the portion of the grate at the discharge end thereof and below said arch.

6. A sprinkler stoker comprising an ash conveyor including a transverse drag member adapted, by moving over the stoker grate, to gather ash from below the fuel bed on the grate and discharge the ash from the grate at one end thereof, said drag member being arranged to reciprocate on the grate longitudinally thereof and shaped to exert a cleaving action when moving away from the discharge end of the grate, and means for separately controlling an air supply to the portion of the grate at the discharge end thereof, said means supplying air to the said portion of the grate at a pressure higher than that of air supplied to the adjacent part of the grate.

CEDRIC H. SPARKS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

